1756-EN2TR Dual-Port Ethernet Bridge Replacement

Overview

The Rockwell Automation Allen-Bradley 1756-EN2TR is a dual-port EtherNet/IP communication module that resides in a ControlLogix chassis. It provides high-speed, 10/100 Mbps communications, allowing controllers to interface with remote I/O, other controllers, HMIs, SCADA systems, and enterprise databases.

Its key design feature is its two physical RJ45 ports that share a single IP address. This internal switch technology supports Device Level Ring (DLR), linear, and star network topologies. Given its vital role as the central communication gateway for critical automated systems, replacing or upgrading this card requires precise methodology to prevent data disruption, network loops, or system faults.

Legacy Product Information

The 1756-EN2TR has served as an industry-standard communication module for many years. It is classified as an active, mature product, meaning it is still produced but has modern replacements available with increased processing capabilities and enhanced security profiles.

Specifications Comparison:

• Catalog Number: 1756-EN2TR
• Backplane Current Draw: 1.0 A @ 5.1 V DC; 3 mA @ 24 V DC
• Power Dissipation: 5.1 W
• Communication Speed: 10/100 Mbps (Full or Half Duplex)
• Logix Connections: Up to 256
• TCP/IP Connections: Up to 128
• CIP Unconnected Messages: 128
• EtherNet/IP Packet Rate Capacity: Up to 25,000 Packet-Per-Second (PPS) for I/O communications.
• Network Topologies: Star, Linear, and Device Level Ring (DLR)
• Common Applications: Distributing remote I/O on DLR loops, handling high-density CIP Motion paths, communicating with remote chassis, and linking HMI/SCADA infrastructure to Logix 5000 CPUs.

Recommended Replacements

When replacing a 1756-EN2TR, you can choose a direct, identical module or upgrade to a higher-capacity interface. The choice depends on performance demands, current network standards, and compatibility constraints.

Compatibility Considerations

Wiring and Physical Footprint

The 1756-EN2TR fits in any slot of a standard ControlLogix chassis (such as the 1756-A4, -A7, -A10, -A13, and -A17 series). Physical dimension alterations are not necessary when upgrading because the successor modules (including the 1756-EN4TR) occupy exactly one slot. The two front-facing RJ45 connectors accept standard Cat5e or Cat6 shielded cables.

Software Requirements

• Studio 5000 / RSLogix 5000: The minimum software version required depends entirely on the slot configuration and electronic keying. RSLogix 5000 Version 16.03 or greater supports the original 1756-EN2TR. Upgrading to a 1756-EN4TR requires Studio 5000 Logix Designer Version 32.00 or higher to leverage its gigabit profiles.
• Add-On Profile (AOP): Ensure that you have the latest module profile pack installed in your Studio 5000 software before performing configuration changes.

Hardware-to-Software Configuration Alignment

When assigning safety or general I/O, pay close attention to electronic keying configuration in Studio 5000:

1. Exact Match: The replacement card must feature the identical catalog number, major revision, and minor revision of the configured card.
2. Compatible Module: The replacement can have a higher major or minor revision than specified, provided the catalog number is the same.
3. Disable Keying: The controller accepts any communication card of the same catalog type regardless of firmware versions (not recommended for high-safety systems).

Hardware Address Settings

Unlike simple network nodes, the module supports three physical rotatory switches on the bottom front edge. If you configure a static IP on the subnet range 192.168.1.xxx, you can set these switches to a value between 001 and 254. If set within this range, the module automatically sets its subnet mask to 255.255.255.0 and its gateway to 0.0.0.0 (unless configured otherwise in software). Alternatively, set the switches to 888 for a factory default reset, or 999 (or other out-of-range numbers) to use internal DHCP/BOOTP memory configuration.

Upgrade Benefits

Upgrading from the legacy 1756-EN2TR to the modern 1756-EN4TR delivers the following enhancements:

• Gigabit Integration: The 1756-EN4TR features 1 Gbps capability, eliminating network collisions, heavy latency, and backplane transfer bottlenecks in systems running multiple Remote I/O and CIP Motion processes.
• Enhanced Security (CIP Security): Built-in hardware capabilities for CIP Security block unauthorized device access, data tampering, and packet-injection attacks at the physical port level.
• Connection Expansion: It doubles the Logix logical connection capabilities from 256 to 512, and expands the TCP/IP connections from 128 to 1,000, allowing more SCADA clients to connect concurrently.

Common Migration Challenges

• Electronic Keying Conflicts: A common pitfall occurs when replacing an older revision (e.g., Series A, Firmware v2.004) with a modern stock card running higher firmware (e.g., Series C, Firmware v10.007). If Studio 5000 is configured for "Exact Match," the CPU will reject communication with the module, generating an I/O connection fault.
• DLR Loop Disruptions: The dual ports on the 1756-EN2TR participate in ring recovery protocols (DLR). Removing a module configured as the "Ring Supervisor" will break the recovery protocol unless an active backup supervisor exists on the network, potentially causing network storms or standard communication losses.
• DHCP/BOOTP Retention Issues: If the static IP setting was written to the non-volatile memory of the module via RSKey, the replacement module must have the IP physical switches set exactly matching, or the software configuration must be rewritten through the DHCP/BOOTP tool.

Step-by-Step Replacement Procedure

Be sure to follow standard electrostatic discharge (ESD) handling practices during this process.

Step 1: Preparation and Backup Induction

1. Connect your laptop to the system and verify the existing network configuration utilizing RSLinx Classic or FactoryTalk Linx.
2. Open the active PLC project file in Studio 5000 and go online with the controller.
3. Take a complete backup of the controller memory before making any physical configuration modifications.
4. Record the module's exact details: Catalog Number, Series, Firmware Revision, and exact IP Configuration (IP, Gateway, Subnet, DNS).

Step 2: Physical Swap (RIUP Supported)

Note: ControlLogix chassis support Removal and Insertion Under Power (RIUP). However, if your module drives primary field elements (valves, motors, safety loops), verify downstream safety protocols.

1. Label each Ethernet cord attached to Port 1 and Port 2 to keep linear or DLR sequences intact.
2. Press the top and bottom retaining tabs inward and pull the legacy 1756-EN2TR straight out of the slot.
3. Check the physical rotary switches on the replacement module. If you are copying a hardware-defined base IP (192.168.1.xxx), match the numbers to the old card. If using DHCP or saved parameters, ensure the switch is set to 999 (or 000).
4. Slide the new card into the chassis slot, and push firmly until the locking tabs snap into place.
5. Reconnect the Ethernet cables to Port 1 and Port 2 as originally labeled.

Step 3: Firmware Configuration and Address Commissioning

1. Open ControlFLASH or ControlFLASH Plus.
2. Select the 1756-EN2TR target and locate it on your networks. If it is factory fresh, you must set an initial configuration IP using the BOOTP/DHCP utility or by utilizing the physical rotary switches.
3. Flash the module to the target firmware version identified in Step 1 to satisfy module electronic keying rules.
4. Verify that you have disabled DHCP/BOOTP inside the network configuration parameters in RSLinx Classic to ensure the card retains its static assignment on power cycle.

Step 4: System Diagnostics and Commissioning

1. Confirm the indicators on the physical faceplate of the newly installed 1756-EN2TR:
   • OK LED: Solid Green confirms internal diagnostics are functional.
   • NET LED: Solid Green indicates that the IP address configuration is complete and connection exists. (Flashing green means it is waiting for an IP address; Red indicating duplicate IP).
   • LINK1/LINK2 LED: Flashing Green confirms active network traffic on the respective ports.
2. Open Studio 5000 and verify that all remote I/O nodes, variable frequency drives, and HMI nodes on the target network show active and run states, with no connection faults visible in the I/O Tree.

Frequently Asked Questions

Q1: Can I replace a 1756-EN2TR with a single-port 1756-EN2T?

A1: Only if your system does not utilize DLR (Device Level Ring) or direct network daisy-chaining (linear network topology). The 1756-EN2T has only one physical port, meaning any ring architecture or downstream daisy-chained devices will lose connections permanently.

Q2: What causes the NET LED on the new module to flash red?

A2: A flashing red indicator typically points to a duplicate IP address conflict on the current network. Disconnect the network cable and check if another IP address poll shows active responses on that address.

Q3: How do I perform a complete factory reset on the module?

A3: Set the physical rotary switches to 888 and cycle the power to the chassis. Once restarted, turn the power off again, change the switches back to your target address parameters (e.g., 999 for software management), and restore power.

Q4: If I upgrade to a 1756-EN4TR, do I have to alter my existing PLC program?

A4: Yes. Because the catalog number is different, you must delete or modify the 1756-EN2TR in the Studio 5000 I/O configuration hierarchy and replace it with a 1756-EN4TR. This hardware alteration is an offline change and requires a download of the modified program to the controller.

Related Products & Families

Within the ControlLogix lineup, the 1756-EN2TR interacts closely with:

• ControlLogix Controllers: 1756-L71, 1756-L72, 1756-L73, 1756-L74, 1756-L81E, 1756-L82E, 1756-L83E, 1756-L85E, and GuardLogix safety controllers.
• Chassis and Power Supplies: 1756-A7, 1756-A10, 1756-PB72, and 1756-PA75.
• Remote I/O Platforms: POINT I/O 1734-AENTR, FLEX 5000 5094-AENTR, and FLEX I/O 1794-AENTR network interfaces.

Need Help?

Whether you require a direct replacement 1756-EN2TR, an upgraded 1756-EN4TR, or standard replacement components to minimize system downtime, Palm Parts Solution can assist. We supply high-quality new, surplus, and thoroughly tested refurbished industrial automation parts, backed by a comprehensive warranty to keep your production systems online and running efficiently. Contact our technical team today for immediate supply support.